1. Field of the Invention
The present invention relates to an ultrasonic motor.
This application is based on Japanese Patent Application No. 2006-343978, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, ultrasonic motors have been drawing attention as a new type of motor replacing electromagnetic motors. Ultrasonic motors have the following advantages over known electromagnetic motors:
1) Ultrasonic motors are capable of high torque without using gears;
2) Ultrasonic motors have holding power when powered off;
3) Ultrasonic motors have high resolution;
4) Ultrasonic motors are quiet; and
5) Ultrasonic motors do not generate magnetic noise and are unaffected by noise.
A known ultrasonic motor is disclosed in, for example, Japanese Unexamined Patent Application, Publication No. HEI-11-235062, as a rotary motor using three transducers formed by bonding a piezoelectric device to an elastic body. According to Japanese Unexamined Patent Application, Publication No. HEI-11-235062, a driving circuit is provided for each transducer to drive each transducer by applying an optimal frequency thereto.